Pipettes, including serological pipettes, are widely used in laboratory to transfer liquid samples. To prevent contamination of suction devices by over pipetting and aerosol contamination, cotton plugs were widely used in serological devices. Cotton plugs are cheap and easy to assemble into the serological pipette. However, cotton plugs do not provide a good aerosol barrier or prevent over pipetting with potential contamination of the pipetting device. Other porous media such as fabric based self-sealing media have been described in the literature (US 2003/0099576). Frusto-conical sintered porous self-sealing plugs have been used as filters in frusto-conical plastic pipette tips (U.S. Pat. No. 5,156,811). However, there have been no commercial products for cylindrical serological pipettes that employ sintered porous plastic plugs. One obstacle preventing use of sintered porous plastic as a serological pipette filter plug is that fast speed insertion methods require perfect alignment of the filter plug and the serological pipette. The assembly of the filter plug into the serological pipette is generally accomplished using high speed automated equipment. If the filter plug and the serological pipette are not properly aligned during assembly, the serological pipette and filter plug can be torn or bent leading to problems in downstream processing, fragmentation of the plug, and potential failure of the device. Current cylindrically shaped pipette filter plugs with sharp edges do not meet high speed insertion requirements because slight misalignment causes shut down of high speed machine assembly machines. What is needed is a plug design that permits rigid sintered porous plastic plugs to be self-centering and self-guiding during the high speed insertion process to improve production efficiency.